Mr Cillian Murphy is hefting a full leather weekend bag and rucksack as he strolls to our lunch in deepest Hackney, London. It’s a signal not only that this least starry of film stars still carries his own luggage, but that, after living here for a decade and a half, he’s no longer a Londoner. He’s just passing through, on the way from his new home in Ireland to Berlin for a film festival.

The Cork-born actor and his wife, artist Ms Yvonne McGuinness, exchanged Queen’s Park NW6 for Dublin in 2015, after deciding it was “time to release a bit of pressure”, he says. “I don’t miss London. There’s only six million people on the whole island of Ireland. It’s just better for your head to have fewer people around, and Irish people are really sound.”

The couple and their sons – Malachy, 11, and Aran, nine – share a Victorian townhouse on the coast south of the Irish capital with a 16-month-old black labrador, whom the boys named Scout after seeing To Kill A Mockingbird. “I’ve always loved labradors,” Mr Murphy says. “They’re so caring and emotionally smart. We walk him on the beach every day. He has the best life.”

Mr Murphy turned 40 last May, and that milestone might have had something to do with his lifestyle taking a more sedate turn. “Most middle-aged men are engaged in some form of self-improvement, like yoga or giving up drinking,” says Mr Murphy, who jogs. “You don’t want to grow old disgracefully, if you can help it.”

Mr Murphy is dressed down in his civvies, which include a blue woollen hat, a blue shirt, a blue knit jacket and blue jeans. “Yeah, my wife gives out a lot about all the blue,” he says. “It’s just safe, man. You can’t go wrong with navy. My taste is very much: a good pair of jeans, a good jacket, a good pair of shoes. Well-made things that fit. I’m not adventurous.”

The blue has the added benefit of matching Mr Murphy’s piercing eyes, the kind that inspire Irish folk ballads, balanced atop his formidable cheekbones like marbles. Different film-makers have seen different things in those distinctive features.

Mr Danny Boyle cast Mr Murphy as a heroic everyman in the zombie flick 28 Days Later and the cult sci-fiSunshine. Mr Neil Jordan cast him as a transwoman in Breakfast On Pluto, while in Peacock, he played a man with multiple-personality disorder, whose alter ego is his own “wife”.

“My taste is very much: a good pair of jeans, a good jacket, a good pair of shoes. Well-made things that fit. I’m not that adventurous”

He has twice portrayed out-and-out psychopaths, for Mr Wes Craven in the thriller Red Eye, and for Mr Christopher Nolan, who cast him as the depraved Scarecrow in the Dark Knight trilogy. Mr Murphy also auditioned for the trilogy’s title role, donning Mr Val Kilmer’s rubber Batman suit for a screen-test that can still be found somewhere on YouTube. “I don’t think I’m the right physical specimen for Batman,” says the actor, who’s a slender 5ft 8in. And besides, “playing the square-jawed hero or the nefarious villain doesn’t really interest me. Humanity falls somewhere in the middle.”

Mr Murphy’s latest role is as a moustachioed IRA man attempting to buy a shipment of guns in Boston in British director Mr Ben Wheatley’s 1970s-set comic thriller Free Fire. The deal goes bad, and the film fast descends into a bloody, blackly hilarious shootout between various crooks played by Ms Brie Larson, Mr Armie Hammer and Mr Sharlto Copley.

Mr Murphy first took notice of Mr Wheatley after seeing his 2011 feature Kill List. “I thought it was a really significant film, so I sought Ben out through my agent,” he says. “We met at a pub and had a few beers. And then we met again, and had another few beers, and I was like, ‘Look, man, whatever you’re doing, I want to be involved.’ And when he wrote Free Fire, he very kindly wrote that part with me in mind.” Mr Wheatley writes and edits his films with his wife, Ms Amy Jump, and the couple shot the film at a disused print works near their home in Brighton. “It was like summer camp,” says Mr Murphy. “It was one of the most enjoyable film shoots I’ve ever been on. Brighton in the summer, just shooting guns and messing. It was fantastic craic.”

Moustache notwithstanding, Mr Murphy still sports almost the same haircut he had in Free Fire, but his locks won’t be long for much longer. In a few weeks, he’s due back on set to shoot the fourth series of the BBC drama Peaky Blinders, for which he routinely wears the short back and sides of a Tommy just back from the trenches.

The Midlands of the 1920s appears to share several style markers with parts of Hackney in the 2010s. Mr Murphy plays the show’s protagonist, gang boss Tommy Shelby, who wears tailored tweed and a flat cap over that distinctive hairstyle, which could also be seen recently on everyone from Macklemore to Ms Miley Cyrus. “I would never voluntarily have that haircut,” says Mr Murphy. “That and the hat, the voice, the walk, the fags – it’s all an effort to make me look like a tough fucker, which I’m really not. I’ve never even been in a fight.”

Tommy Shelby is Birmingham’s answer to The Godfather’s Michael Corleone. Violent and ruthless, yet fiercely loyal and with a concealed capacity for tenderness, he was decorated for his heroism during WWI, but brutalised by his experience there. Mr Murphy and the show’s creator, Mr Steven Knight, “worked hard to show that this man had a history”, he says, “that the war was the defining moment of his life, and that there was a pre- and a post-war Tommy. That’s a brilliant platform for a character – a man who’s been altered by something you and I could never even conceive. He’s multi-faceted, multi-layered. He’s fascinating to play.”

Mr Murphy orders mineral water and a cheeseburger for lunch. I’d read that he was a vegetarian, but it turns out meat is one thing he’s taken up again as he approaches middle age. “I was vegetarian for about 15 years,” he says. “But it was never a moral decision. It was more that I was worried about getting mad cow disease. For the first series of Peaky Blinders, they were anxious that I shouldn’t look like a skinny Irish fella, and my trainer recommended meat.”

“It was one of the most enjoyable shoots I’ve ever been on. Brighton in the summer, just shooting guns and messing. It was fantastic craic”

So, what was his first taste of flesh after the long fast? A bacon sandwich? Mr Murphy laughs. “Actually, it was a venison steak,” he says. He and some friends were at a country house hotel in Ireland celebrating his wife’s 40th birthday. “A few cocktails had been had before dinner. When the waiter asked if I’d like the fish or the venison, I hesitated and he said, ‘Have the venison.’ He was right. It was extraordinary. They reared their own deer on the property.”

His ears prick up at the sound of a live band practising in the pub’s back room. Music was Mr Murphy’s first passion. The eldest of four siblings, as a teenager he started a band with his brother Padraig and some Cork school-friends. In 1996, The Sons Of Mr Greengenes (as the band was called) were offered a five-album deal by the London label Acid Jazz.

They turned it down. “My brother was still only 16, so my parents wouldn’t allow him to sign his life away,” says Mr Murphy. “And we didn’t want to do it without him. Anyway, the deal was terrible. It was like, ‘Come to London and live in digs somewhere on 50 quid a week, and we’ll own all of your music.’ So that was our peak, and then it fizzled out.”

It was at one of the band’s gigs that he first met Ms McGuinness, whom he married in 2004. Today he still owns several guitars and “dabbles” in music, but “purely as a hobby”. If he has a vice, he says, it’s spending too much on records. “The last album I bought was a jazz record by Nels Cline, the guitarist from Wilco,” he says. “I have a friend who says that what he loves about vinyl is the inconvenience and the expense. But, you know, it actually does sound better.”

With the prospects of a recording career receding, Mr Murphy was halfway through the first year of a law degree at University College Cork (“Why the fuck I was studying law, I don’t know”) when he attended his first professional theatre performance, an elaborate production of A Clockwork Orange, staged by the Cork-based Corcadorca theatre company.

“The haircut and the hat, the voice, the walk, the fags – it’s all an effort to make me look like a tough fucker, which I’m really not”

Inspired, he lobbied Corcadorca for an audition, and was eventually awarded the male lead in Disco Pigs, by the then little-known playwright, Mr Enda Walsh. The production was a breakout success, which ended up touring the world and being made into a movie, with Mr Murphy reprising his role as Pig, an impassioned and explosively violent Irish teenager.

“Disco Pigs had a huge impact on my taste, and on my life,” says Mr Murphy, who has gone on to perform in two more of Mr Walsh’s plays, Misterman and Ballyturk, and says he’d like to work again with the playwright, who is now a close friend. “I haven’t read anything of late that’s as exciting as Enda’s work. I’ve never been interested in classical plays. People think that’s a terrible thing for an actor to say, but if you do Shakespeare, you’re only going to be compared to actors who’ve already done it wonderfully. Maybe, as I get older, I’ll get less hung up on that. I’ve done Chekhov and Playboy Of The Western World, so I’ve ticked a few of those boxes, but what excites me is new writing.”

On screen, Mr Murphy has also cultivated regular collaborators, such as Mr Boyle and Mr Nolan, with whom he has now made five films – Inception and the forthcoming WWII epic, Dunkirk, on top of the Dark Knight trilogy. Though the details of Dunkirk remain mostly under wraps – the film isn’t out until July – Mr Murphy says he shot many of his scenes in Holland with Sir Mark Rylance.

Quite apart from being a “phenomenal man”, Mr Murphy says Sir Mark was also partially responsible for his own return to the stage, with Misterman in 2011. “He’s a legend. I’d seen him in Jerusalem [in 2009] and it knocked me for six. It reignited my love for theatre. I hadn’t been on stage for about six years and his performance was part of the reason I went back to it.”

“I’m a European. I like seasons. And, like most Irish men, I probably look better in a pair of trousers than a pair of shorts”

After our interview, Mr Murphy is off to catch a plane to the Berlin Film Festival to promote another new project, director Ms Sally Potter’s black comedy of contemporary manners, The Party, in which he plays a coke-snorting financier. The actor’s life often keeps him away from home for half the year or more. Each series of Peaky Blinders alone takes four months to shoot.

There was a time when he could probably have chosen to move to Hollywood and the dark heart of the movie business, but he was never tempted. “I love the sun and the food and the sea,” he says. “But LA’s not for me. I’m a European. I like seasons. And, like most Irish men, I probably look better in a pair of trousers than a pair of shorts.”

Then again, there was also a time when he thought he’d never move home to Ireland, either. “It’s the classic Irish narrative, to go away and return,” he says. “If you’d told me when I left at the age of 20 that one day I’d move back, I’d have said, ‘No way, I’m never going back.’ But 19 years later, it felt like the most natural thing to do.”